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THE BASIC OPEN-HEARTH PROCESS.                       197
slag will be increased, in spite of the cutting of the hearth. This latter action is a correcting condition, but is not the controlling influence., as is proven by the small amount of scorification.of the hearth during oreing. The real determinant is the carbon of the bath, and there is an equilibrium between the oxidizing power of the flame, the reducing power of-the metalloids, and the struggle after fluidity. • ..............-                                        ..... -
In the basic process there is difficulty in making a slag entirely of silicate of lime, for this is more viscous than a slag of the same percentage of silica containing other bases; there is a tendency, therefore, toward, the absorption of iron oxide, but this is. opposed by a contest on the part of the lime for the possession of the silica, and the result is; a decrease in the percentage of iron when there is an increase in lime. Inasmuch as the substitution of Cab "for FeO produces a more viscous slag, this would seem to invalidate the theory just, advanced, 'but the effect is due not to a change in the law, but to the action of stronger forces. The more bases present, the less necessity is there for an additional amount, since the weight of silica necessarily remains constant, • and, as the reducing action of the metalloids comes into play, the slag begins to be robbed of its iron, which at the same time is its 'most reducible and its most fusible base. The presence of oxide of manganese in the slag modifies without completely changing the relations just described, for, by furnishing an additional base and imparting greater 'fluidity, it tends to render the-presence of iron oxide less necessary.
SEC. Xli—:Automatic regulation of fluidity.—Fluidity is of vital-practical importance, for the slag must run freely from the furnace, else the hearth will soon be filled; furthermore, the.slag must be so basic that the hearth is not scorified. The two conditions, fluidity, and basicity, determine the nature and amount of the basic additions, for the sum of CaO and MgO cannot much exceed 55 per cent, without producing a viscous cinder, neither can the percentage of Si02.fa;ll below 10 per'cent., unless unusual amounts are present of the oxides of iron, manganese, or .phosphorus. This theory of 'the automatic regulation 'of fluidity seems to account for a curious relation between the content of Si02 and FeO in a large number of-basic slags,/which are grouped in Table XI-D.
The phosplwric, acid was not .determined, but it -may, b® taken for granted that; an increased proportion of phosphorus in the dharge